The present invention relates to a thermal printer, and more particularly to a structure of the thermal printer and a structure of a paper detecting sensor.
The thermal printer in which characters are formed by heating selected elements of a dot matrix that is in contact with heat-sensitive paper is widely used in printers such as the facsimile receiver.
U.S. Pat. No. 5,150,130 discloses a label printer and U.S. Pat. No. 5,422,660 discloses a label printer using a transfer ribbon.
In a printer for printing bar codes on label paper, a sensor is provided for detecting the position of the label paper as disclosed in U.S. Pat. Nos. 4,706,096 and 4,757,329. The paper detecting sensor is mounted on a paper passage. There are two types of the paper detecting sensor. One is the transmitting type sensor and the other is the reflection type sensor. The paper detecting sensor detects the position of the label paper by detecting a black line or notch formed in a mount or label paper.
There is also used a slide type sensor comprising a pair of members which are opposite set at a position corresponding to the notch of the recording paper.
In the conventional printer using the transfer ribbon, the paper and ribbon must be passed through a narrow gap, and then set at predetermined positions. Consequently, it is difficult to set the paper and ribbon.
On the other hand, a cutter is mounted on the printer, the paper is fed to the cutter and cut by the cutter. Thereafter, the paper is fed back to the printing position. At that time, the ribbon fed back together with the paper is liable to be loosened to cause the ribbon to be wrinkled.
The recording paper is inserted between opposite members of the paper detecting sensor. However, since the members are closely disposed at a small space of 2 or 3 mm, it is troublesome to insert the paper.
Furthermore, if the label peels off and adheres to the paper detecting sensor, the label must be removed. However, it is difficult to remove the label, because the space between opposite members of the sensor is very narrow.